Picture frame



FIG. 1 is a perspective view of a picture frame showing my new design;

FIG. 2 is a front view thereof, the rear view being identical;

FIG. 3 is a right side view thereof, the left side view being identical; and,

FIG. 4 is a top view thereof.

The bottom view is omitted and forms no part of the claimed design. 

The ornamental design for a picture frame, as shown and described. 